(a) Field of the Invention
The present invention relates to a receiver for a MIMO (Multiple-Input Multiple-Output) antenna CDMA (Code Division Multiple Access) system. More specifically, the present invention relates to an adaptive MMSE (Minimum Mean Square Error) interference suppression receiving apparatus for a space-time block coded DS (Direct Sequence)/CDMA communication system.
(b) Description of the Related Art
In general, the MIMO antenna system is a communication system that transmits space-time block coded data via multiple transmitter antennas after data spreading with a different code by users, and receives data from users via multiple receiver antennas.
The conventional technologies concerning the structure of a receiver for the space-time block coded MIMO antenna system are disclosed in the following documents: Ref. 1: S. M. Alamounti, A simple transmitter diversity scheme for wireless communications, IEEE J. Select. Areas Commun., vol. 16, pp. 1451–1458, October, 1998; Ref. 2: V. Tarokh, H. Jafarkhani, and A. R. Calderbank, Space-time block codes from orthogonal designs, IEEE Trans. Inform. Theory, vol. 45, pp. 1456–1467, July 1999; and Ref. 3: A. F. Naguib, N. Seshadri, and A. R. Calderbank, Increasing Data Rate Over Wireless Channels, IEEE Signal Processing Magazine, vol. 17, No. 3, pp. 76–92, May 2000.
Ref. 1 and Ref. 2 disclose a space-time block coded TDMA system using two transmitter antennas, an optimal block coding transmission method for a system using at least two transmitter antennas, and a maximum likelihood receiver for the same.
The maximum likelihood receiver proposed in the two references can be applied for space-time block coded DS/CDMA systems and can provides an antenna diversity gain proportional to the product of the number of transmitter antennas and the number of receiver antennas, thereby guaranteeing an excellent data detection performance relative to general Rake receivers.
But the maximum likelihood receiver, which is devised on the assumption that the interference signal and the background noise other than the desired user's transfer signals are AWGN (Additive White Gaussian Noise), has a deterioration of performance in a MAI (Multiple Access Interference) environment.
On the other hand, the receiver of Ref. 3 is designed to enhance a reception performance by eliminating interference signals of other users under a circumstance in which multiple users are present in the TDMA system after space-time block coding. But the receiver has a loss of receiver antenna diversity in the order of as much as the number of interference signals to be removed, causing a deterioration of reception performance.
The above reception methods for the space-time block coded TDMA communication system can be expanded to the reception method for the space-time block coded DS/CDMA communication system with a little modification. However, the maximum likelihood receiver has a deterioration of performance due to the MAI that inevitably occurs in the CDMA environment when multiple users share a single channel, and the interference suppression receiver of Ref. 3 has a deterioration of data detection performance caused by a loss of diversity gain.